Refrigerators with a non-azeotropic mixtures of hydrocarbons refrigerants

ABSTRACT

A refrigerant circuit using a non-azeotropic mixture of hydrocarbons refrigerants comprises a compressor, a condenser, an expansion device, a first evaporator downstream the expansion device, a second evaporator downstream the first evaporator, a first heat exchanger to cause heat exchange between refrigerant downstream the condenser and upstream the first evaporator, on one side, and refrigerant downstream the first evaporator and upstream the second evaporator, on the other side, and a second heat exchanger to cause heat exchange between refrigerant downstream the condenser and upstream the first heat exchanger, on one side, and refrigerant downstream the second evaporator and upstream the compressor, on the other side, the expansion device having a capillary tube as part of both heat exchangers as a side of exchangers, the capillary tube being parallel to and in contact with a tube of the circuit or it is wrapped around such tube.

RELATED APPLICATION(S)

This application claims the priority benefit of European Patent Application 13187230.1, entitled “Refrigerator with a Non-Azeotropic Mixture of Hydrocarbons Refrigerants,” and filed on Oct. 3, 2013, the entirety of which is incorporated herein by reference.

BACKGROUND

A “dual evaporator” or “sequential evaporator” refrigerator has a refrigerant circuit including a compressor, a condenser, an expansion device, a first evaporator downstream the expansion device, a second evaporator downstream the first evaporator, a first heat exchanger to cause heat exchange between refrigerant downstream the condenser and upstream the first evaporator, on one side, and refrigerant downstream the first evaporator and upstream the second evaporator, on the other side, and a second heat exchanger to cause heat exchange between refrigerant downstream the condenser and upstream the first heat exchanger, on one side, and refrigerant downstream the second evaporator and upstream the compressor, on the other side. Such refrigerators may use a refrigerant including a non-azeotropic mixture of hydrocarbons.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and features of refrigerators according to the invention will be clear from the following detailed description, provided by way of non limiting examples, with reference to the attached drawings in which:

FIG. 1 is a schematic view of a refrigerant circuit of a refrigerator according to the invention;

FIG. 2 is a detail of a cross-section of one of the two heat-exchangers of FIG. 1 according to a first embodiment; and

FIG. 3 is a detail similar to FIG. 2 and referring to a second embodiment of the invention.

DETAILED DESCRIPTION

Some “dual evaporator” or “sequential evaporator” refrigerators use a non-azeotropic mixture of two different refrigerants, for instance propane (R-290) and n-butane (R-600), which has an appropriate gliding temperature difference (GTD) during evaporation and condensation phases. With a refrigeration cycle using the above mixture, known also as Lorenz-Meutzner cycle, it is possible to have substantially identical or at least similar energy saving performances of a dual evaporator refrigeration circuit using a mono-component refrigerant and a by-pass two-circuit cycle, where a 3-way electrovalve is used.

A refrigerator of the type mentioned above is disclosed by U.S. Pat. No. 5,207,077 and European Patent Publication EP 2 592 366, both of which are incorporated herein in their entirety. In both of the above documents, the expansion device is placed immediately upstream the first evaporator, i.e. the low-temperature evaporator. In U.S. Pat. No. 5,207,077 the expansion device is identified in the drawing as an expansion valve, while in EP 2592366 the expansion device is a capillary tube arranged at the side of the first evaporator. In the first solution the presence of the valve does increase the overall cost of the appliance, and it may create problem of condensation on suction tube. In the second solution, as it is also disclosed in “Performance optimization of a Lorenz-Meutzner cycle charged with hydrocarbon mixtures for a domestic refrigerator-freezer”, International Journal of Research (UR) N. 35, Issue 1, Jan. 2112, pages 36-46, the optimum capillary tube length is of the order of 10-15 m if similar energy consumption performances of a bypass two-circuit cycle are to be obtained. UR N. 35, Issue 1, Jan. 2112, pages 36-46 is incorporated herein in its entirety.

In the above documents the sub-cooling from second evaporator and compressor and the additional one required using these mixtures (tube connection between first and second evaporator) is obtained through use of heat exchangers made with two tubes. In EP 2 592 366 it is explained that these tubes work better in case one is inside the other and in counter-flow.

The above mentioned publication and patents give indications on modifications required by a refrigerator/freezer product using a non-azeotropic mixture. The above mentioned article “Performance optimization of a Lorenz-Meutzner cycle charged with hydrocarbon mixtures for a domestic refrigerator-freezer” also provide information on modification in length of capillary (required at least 10 meters (m)) in order to have benefits in energy and correct behavior of product.

Disclosed herein are refrigerators with refrigeration circuits designed for a modified Lorenz-Meutzner cycle which does not present the above problems and has a low cost. Disclosed examples use a capillary tube for the two heat exchangers required for this cycle. In other words, the capillary tube is used as one side of both heat exchangers. In some examples, the capillary tube is used externally to the other tubes of the refrigerant circuit, and the refrigerant flow in the capillary tube is in counter flow with reference to the refrigerant flow in the tube of the refrigerant circuit. According to other examples, the capillary tube is used internally to the other tube.

According to some embodiments, the capillary tube has a length between 2.5 m and 5 m, and an internal diameter between 0.6 and 0.8 millimeters (mm).

The use of a capillary tube with a reduced length reduces the overall cost of the appliance and increases the simplicity of the layout of the refrigerant circuit, with related advantages in term of reliability and reduced overall volume of the circuit.

Even though different kinds of refrigerant mixtures can be used, a mixture of 80% and 20% by mass in liquid phase of n-butane and propane respectively has the advantage of not requiring a different compressor (i.e., the same for iso-butane R600a can be used).

With reference to the drawings, the refrigerant circuit according to the invention comprises a compressor 10, a condenser 12, usually placed on back wall of the refrigerator, cooled by natural convection or with forced air, and a drier 14 as normally used on a domestic refrigerator/freezer appliance.

Downstream the drier, the circuit comprises a capillary tube 16 preferably having a length between 2.5 m and 5 m (depending on the total volume of the cells, the type of compressor etc.), with an internal diameter comprised between 0.60 mm and 0.80 mm.

The circuit comprises a first heat exchanger 18 and a second heat exchanger 20. The first heat exchanger 18 present a first side made by a capillary tube portion 16 a in contact with a portion 22 of the circuit tube between first or low temperature evaporator 17 (placed in the freezing compartment—not shown) and second or high temperature evaporator 19 (placed in the refrigerating compartment—not shown). The section of such heat exchanger is shown in FIG. 2, and the length of this tube/tube heat exchanger is preferably between 0.5 m and 1 m. Internal diameter of the suction tube 22 is preferably between 5 and 8 mm.

As shown in FIG. 2, the capillary tube portion 16 a and the portion 22 of the refrigerant circuit tube are in heat-exchange contact one with another, and they are covered by a layer of aluminum foil 23 which may be a self-adhesive aluminum tape which assures a correct placement of the two parts of the heat exchanger and helps increasing the thermal efficiency thereof.

According to a further embodiment shown in FIG. 3, the capillary tube 16 a is wrapped around and in heat-exchange relationship with the tube 22 of the refrigerant circuit, without use of any aluminum layer.

The second heat exchanger 20 is similarly composed of a capillary tube portion 16 b and a portion 24 of suction tube upstream the compressor 10. The length of such double-pipe heat exchanger 20, particularly in the embodiment shown in FIG. 2, is preferably between 1.5 m and 3 m. Internal diameter of the suction tube 24 is preferably between 5 mm and 8 mm. The section of the second heat exchanger 20 is identical to the section of the first heat exchanger 18 shown in FIG. 2 or 3.

For the first evaporator 17 (freezing evaporator—low temperature), the same evaporator used in refrigerators with the bypass two-circuit cycle (where aR600a is used as refrigerant) can be adopted. For the second evaporator 19 (refrigerating Evaporator—high temperature), an increased surface of about 10/30% vs. the surface of an evaporator used in a bypass two-circuit cycle is beneficial for energy saving performances.

The use of capillary 16 also as a second heat exchanger tube 16 b improves the sub-cooling of the tube connection from second evaporator 19 (at high temperature) and compressor 10. In the disclosed examples, it is possible to have equivalent or even improved energy reduction compared to prior art, particularly EP 2 592 366, but with a length of capillary reduced (less than 5 m) and with a reduced length of suction tube (tube connection between high temperature evaporator and compressor of less than 3.5 m), simplifying the refrigerant cycle and reducing the overall cost of the appliance.

Solutions according to the invention can be applied to direct cooled evaporator products (static evaporators in freezing and refrigerating compartments) and hybrid products (no frost freezing and static refrigerating).

In a refrigerator (with freezing and refrigerating compartments) having a total internal volume around 300 liters, benefits obtained applying the cycles according to the invention on a bottom mount freezer built-in product are as follows:

a) Energy Saving

Refrigerator/Freezer Refrigerator Freezer Direct Hybrid Cooled Reference using R600a 920 (*) 860 (*) (watt hour (WH)/24 hours(h)) Result obtained using 814 (*) 770 (*) mixture R290/R600 (20/80) (WH/24 h) Energy Benefit 11.5% 10.5% (*) According standard BS EN 62552 “Household Refrigerating Appliances. Characteristics and Test Methods”

Therefore an energy reduction around 11% has been obtained on both typologies of products.

b) Low Temperatures in Freezing Compartment

Comparison of temperatures obtained in freezer (in air), having compressor running 100% at 32° C. ambient:

Refrigerator/ Refrigerator Freezer Freezer Hybrid Direct Cooled Reference with R600a (° C.) −29.8 −29.6 Result obtained using mixture −32.0 −35.6 R290/R600 (20/80) (WH/24 h) (° C.)

Low temperatures in freezer have not only a positive impact on energy saving performances, but they improve the freezing ability of products in term of capacity (more quantity can be frozen on product in the same time) and in quality (faster freezing improves the quality of food frozen).

In addition the disclosed use of the mixture of refrigerants is able to maintain the same level of noise and of electrical performances of products.

Although certain example methods, apparatus and articles of manufacture have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus and articles of manufacture fairly falling within the scope of the claims of this patent. 

What is claimed is:
 1. A refrigerant circuit using a non-azeotropic mixture of refrigerants, the circuit comprising: a compressor; a condenser; an expansion device; a first evaporator downstream the expansion device; a second evaporator downstream the first evaporator; a first heat exchanger to cause heat exchange between refrigerant downstream the condenser and upstream the first evaporator on a first side, and refrigerant downstream the first evaporator and upstream the second evaporator on a second side; and a second heat exchanger to cause heat exchange between refrigerant downstream the condenser and upstream the first heat exchanger on a first side, and refrigerant downstream the second evaporator and upstream the compressor on a second side, wherein the expansion device comprises a capillary tube adapted to act as the first side of both heat exchangers.
 2. A refrigerant circuit as defined in claim 1, wherein the first and second heat exchangers are each shaped as a double-pipe exchanger formed by the capillary tube in a heat exchange relationship with portions of respective circuit tubes of the first and second heat exchangers.
 3. A refrigerant circuit as defined in claim 2, wherein the capillary tube is externally in contact with the portions of the circuit tubes.
 4. A refrigerant circuit as defined in claim 3, wherein the capillary tube is at least partially wrapped around the portions of the respective circuit tubes of the first and second heat exchangers.
 5. A refrigerant circuit as defined in claim 3, wherein the first and second heat exchangers are each covered by an aluminum layer.
 6. A refrigerant circuit as defined in claim 2, wherein the capillary tube has a total length between 2 meters (m) and 5 m.
 7. A refrigerant circuit as defined in claim 2, wherein the capillary tube has an internal diameter comprised between 0.6 millimeters (mm) and 0.8 mm.
 8. A refrigerant circuit as defined in claim 2, wherein the length of the first heat exchanger is between 0.5 meters (m) and 1 m.
 9. A refrigerant circuit as defined in claim 2, wherein the length of the second heat exchanger is between 1.5 meters (m) and 3 m.
 10. A refrigerant circuit as defined in claim 2, wherein the first and second heat exchangers are each covered by an aluminum layer.
 11. A refrigerant circuit as defined in claim 1, wherein the first and second heat exchangers are each covered by an aluminum layer.
 12. A refrigerant circuit as defined in claim 1, wherein the first and second evaporators comprise static evaporators placed in a freezing compartment and in a refrigerating compartment, respectively.
 13. A refrigerant circuit as defined in claim 1, wherein the second evaporator comprises a static evaporator placed in a refrigerating compartment, and the first evaporator comprises a no-frost evaporator placed in a freezing compartment.
 14. A refrigerant circuit as defined in claim 1, wherein the refrigerant comprises a mixture of propane and butane of 20 to 80% by mass in liquid phase. 